(a) Field of the Invention
The present invention relates to a low dielectric material essential for a next generation electric device such as a semiconductor device, with a high density and high performance. More specifically, the present invention relates to: a process for preparing an organic silicate polymer that is thermally stable and has good mechanical and crack resistance properties, and a coating composition for forming a low dielectric insulating film; and a process for preparing a low dielectric insulating film using the organic silicate polymer prepared according to the process, and an electric device comprising the low dielectric insulating film prepared according to the process.
(b) Description of the Related Art
The semiconductor industry is moving toward increasing device complexity, requiring shrinking geometric dimensions and higher component integration with greater dimensional densities in integrated circuit devices, e.g. memory and logic chips. This has led to an increase in the number of wiring levels and a reduction in wiring pitch to increase the wiring density. Current leading-edge logic processors have 7-8 levels of high density interconnect, and interconnect line widths are scheduled to decrease to 0.1 μm around the year 2005.
As device dimensions shrink to less than 0.25 μm, propagation delay, crosstalk noise, and power dissipation due to resistance-capacitance (RC) coupling become significant. The smaller line dimension increases the resistivity of metal wires, and the narrow intermetal spacing increases the capacitance between the metal wires. Thus, although the switching speed of devices will increase as the feature size decreases, the interconnect delay becomes the major fraction of the total delay and limits the overall chip performance. Accordingly, in order to prepare a chip having high speed, a conductor having a low resistance and a dielectric material having a low dielectric constant should be used. In addition, the use of low dielectric material can remarkably decrease the power dissipation and crosstalk noise.
Recently, several semiconductor device manufacturers have put test products on the market that show improvements in their performance of 20% or more, using copper wiring with high electric conductivity instead of using the conventional aluminum wiring. A shift to use of new materials that exhibit low dielectric constant performance, for use in interconnects, has recently been undertaken. If the dielectric films between interconnect layers in integrated circuits can make use of these materials, the effect on operating speed will be the same as that which resulted with the switch from aluminum to copper technology. For instance, if the dielectric constant of the dielectric material is changed from 4.0 to about 2.5, IC operating speed will be improved by about 20%.
The interlayer dielectric material used in semiconductor integrated circuit devices is predominantly SiO2, which is generally formed using chemical vapor deposition (CVD) to withstand various processing operations associated with the conditions under which a dielectric is formed. The dielectric constant of silicon thermal oxidation films, which have the lowest dielectric constant, is on the order of 4.0. Attempts have been made to reduce the dielectric constant by introducing fluorine atoms into an inorganic film deposited by CVD. However, the introduction of fluorine atoms in large amounts decreases the chemical and thermal stability, so the dielectric constant achieved in actual practice is on the order of 3.5. Fluorinated oxides can provide an immediate near-term solution and a shift to new types of insulating materials with sub-3 dielectric constant may be required.
One class of candidates is organic polymers, some of which have a dielectric constant of less than 3.0. Incorporating fluorine into such organic polymers is known to further lower the dielectric constant. Most organic polymers do not, however, posses the physico-chemical properties required for on-chip semiconductor insulation, particularly thermal stability and mechanical properties (sufficient to withstand back-end line-fabrication temperatures within the range of 400˜450° C.). Few organic polymers are stable at temperature greater than 450° C. They also have a low glass transition temperature and thus elasticity thereof remarkably decreases at high temperatures, and they have a very high linear expansion coefficient. Since the temperature rises to 450° C. during semiconductor IC integration and packaging processes, the resulting low thermal stability and elasticity and high linear expansion coefficient can deteriorate the reliability of the devices.
Recently, in order to solve thermal stability problems of organic polymers, the development of organic silicate polymers using a sol-gel process has emerged. In particular, organic SOG (Spin On Glass), having a dielectric constant in the range of about 2.7˜3.3, has been proposed for use as interlayer dielectrics in which the side chain of an organic component (an alkyl group such as methyl) is bonded to the backbond chain of a siloxane bond.
There have so far been known various methods for producing organic silicate polymers such as polyalkylsilsesquioxane for use as a protective film, an interlayer insulating film, etc. for electronic parts or semiconductor elements. General methods for the synthesis of organic silicate polymers are to hydrolyze and condense a silane precursor in a single organic solvent or mixture of organic solvents. The structure of organic silicate polymers-has been reported as a random structure, ladder structure, cage structure, and partial cage structure. In particular, the polysilsesquioxane which contains 1.5 oxygen atoms per silicon atom has a high level of cage or ladder structure and poor mechanical properties. For instance polymethylsilsesquioxane typically has poor mechanical properties. It experiences crack formation during processing unless the film is very thin (often <1 μm).